Fluid-type absorption dynamometers have proven useful in various applications. For example, air absorption dynamometers of suitable construction have been useful in the field-testing of aircraft engines, and, particularly, helicopter engines. As will be appreciated, a dynamometer capable of using air as the working fluid is especially desirable for field-testing in that the supply, storage, and use issues (e.g., freezing) of alternative fluids are eliminated.
Some fluid-type absorption dynamometers, such as disclosed in U.S. Pat. No. 4,744,724, have provided a movable shroud to selectively occlude the blades of a driven impeller that absorbs power from the load under test. With such a movable shroud, the power absorbed by the device may be changed at any operating rotational speed. Despite this advantage, impediments to a wider adoption of fluid-type absorption dynamometer technology have remained. One such impediment has been a restricted power range for which a given dynamometer is usable. A wider range, of course, would be desirable since it would permit a single dynamometer to be used in testing a wider range of engine designs having a wider range of shaft-horsepower outputs.